The present invention relates to a hydraulic stretching device for a saw chain used in a sawing apparatus with a saw bar and includes a holder, a driving wheel arranged at the holder for the saw chain, and a guiding part permanently arranged at the saw bar to interact with the holder and allow the stretching of the saw chain running around the driving wheel and the saw bar.
When mechanized means are used to improve the efficiency of logging operations, it is preferable to use what is known as a timber cutting unit comprising a sawing gear that includes a saw chain and a saw bar. Efficient logging puts high demands on the equipment used with regard to safety, robustness and case-of-use as well as precision and performance, i.e. that the equipment should work speedily and distinctly.
It is well known that a saw chain that rotates under such conditions with high speed around a saw bar in a sawing device requires chain tightening at relatively short intervals. In addition, it is also known that the problem of chain tightening can be solved by an automatic and continuous tightening of the saw chain. This is achieved by making the saw bar displaceable in the longitudinal direction of the saw bar in relation to the driving wheel of the saw chain. However, the chain-tightening force must not be too great, as too great a tension increases the wear on the chain and shortens the working life of both the saw chain itself and the wheel around which the saw chain runs at the free end of the saw bar. It is also known to arrange a hydraulically influenced piston that is active in line with and parallel with the longitudinal direction of the saw bar to accomplish the displacement of the saw bar that stretches the saw chain.
In addition, to ensure good performance, the saw bar that is arranged to be displaced in its longitudinal direction should be distinct and not be allowed to have any free play. The occurrence of play in the parts that move in relation to one another during displacement has been shown to be overcame with known technology by means of hydraulic clamping pistons acting across the direction of displacement of the saw bar. These act to grip and stabilise through pressing the parts that move in relation to one another against one another, thereby counteracting free play. This means, however, that the arrangement has to be provided with additional hydraulic piston, which take up space and need to be connected to the hydraulic system, and which means increased costs for manufacture and later for service and maintenance. Each hydraulic piston is a potential source of leakage.
The objective of the present invention is to overcome the disadvantages stated above and achieve a device for stretching a saw chain that, using only one hydraulic piston, partly stretches and partly stabilizes by gripping the parts that move in relation in one another in the displaceable connection between the holder and the saw bar.
The objective is achieved with a hydraulic stretching device for a saw chain in a sawing apparatus having a saw bar and comprising:
(a) a holder; (b) a driving wheel for the saw chain arranged essentially stationary in relation to the holder, the saw chain being adapted to travel around the driving wheel and saw bar;
(c) a guiding part permanently arranged at the saw bar to interact with the holder and resist turning, the guiding part and the saw bar being axially displaceable in relation to the holder in a direction of a longitudinal axis of the saw bar to allow stretching of the saw chain travelling around the saw bar and the driving wheel;
(d) a hydraulically influenced piston arranged in a displaceable manner at the holder in parallel with the longitudinal axis of the saw bar, the piston having an engaging surface adapted to engage an opposing surface on the guiding part, the engaging surface and the opposing surface are located in parallel planes and these planes are arranged at an angle to a plane perpendicular to the longitudinal axis of the saw bar, whereby when the piston causes the surfaces to engage, the piston influences the guiding part with a force F whose components act partly in a direction of the longitudinal axis of the saw bar to stretch the saw chain and partly in a direction across the direction of the longitudinal axis of the saw bar to achieve a stabilizing gripping of the saw bar, holder and guiding part that move in relation to one another; and
(e) compressible means arranged to engage between the piston and the guiding part before the engaging and opposing surfaces engage one another, whereby an initial stretching of the saw chain is achieved before the combined stretching and gripping effect of the force F is realized.
Further features and advantages of the invention will become evident from the following detailed description of preferred embodiments of the invention that constitute examples and, as such, are not limiting for the scope of protection of the invention.